60-GHz PLL-Based Modulator Boosts Radar Applications

Significant research efforts have been made to realize a cost-effective CMOS IC radar for automotive, security, and presence-detection applications. At 60 GHz, sufficient bandwidth is available to achieve the range resolutions needed for high-resolution velocity detection. To realize this capability, Wanghua Wu, Robert Bogdan Staszewski, and John R. Long from Marvell Semiconductor Inc. have designed and implemented a 60-GHz frequency-modulated, continuous-wave (FMCW), digitally intensive transmit modulator. This modulator is based upon a multi-rate, all-digital phase-locked-loop (PLL) architecture.

In addition to sophisticated equipment, 60-GHz test benches often require on-die probing techniques to extract signals from the IC under test.

To improve the system’s chirp linearity, a high-rate digitally controlled oscillator (DCO) clock is used. This DCO is realized from switched-metal capacitors, which are distributed across a transformer-coupled resonator for a 10% tuning range with roughly 1-MHz resolution at 60 GHz. This feature allows the modulated paths to have clock-cycle precision in time.